regexpowershell

powershell Regex - match only the strings that starts with one occurrence of special chars

I've a file that contains:

# cat
######## foo
### bar
#################### fish
# dog
##### test

with 'Get-Content file.txt | Select-String -Pattern "^#"' I match all those lines... How to get only the lines that starts with only one "#"? (the lines with cat and dog)

Solution

  • You could follow it up with a [^#], so:

    See: https://regex101.com/r/YawMDO/1.

    @'
# cat
######## foo
### bar
#################### fish
# dog
##### test
'@ -split '\r?\n' | Select-String '^#[^#]'

    You could also use a negative lookahead: ^#(?!#), see https://regex101.com/r/9YHjkB/1.

    ... | Select-String '^#(?!#)'

    Yet another option could be to use Select-String -NotMatch with a pattern that matches a string starting with 2 or more #:

    ... | Select-String -NotMatch '^#{2,}'